1. Field of the Invention
The present invention relates to a machining apparatus machining a workpiece by a numerical controller having a program to use a writing method that achieves to compound control amounts from plural programs for driving each of arbitrary axes.
2. Description of the Related Art
It is well known that there are several cutting machines for cutting portions of a workpiece rotatably supported by a headstock and a tailstock. Where a complete circle is formed on a peripheral profile of the cut portions of the rotated workpiece, it is performed relatively simple cutting to in-feed (hereinafter called as infeed) gradually a cutting tool toward the workpiece in a perpendicular direction (hereinafter called as “X-axis direction” or “X-axis”) to a rotated axis (hereinafter called as “C-axis direction” or “C-axis”) of the workpiece.
However, where a cut position of the peripheral of the workpiece is variable according to a rotational angular position of the workpiece such as non-circular cam surface of a cam shaft, a crankpin of a crankshaft, and so on, it needs quite complex cutting to infeed and retract the cutting tool toward and away from the workpiece along the X-axis according to the rotational angular position of the supported workpiece around the C-axis, so called as a C-X profile motion. The “C-X profile motion” is hereinafter defined as the infeed and retract motion of the cutting tool along the X-axis (perpendicular to the C-axis) according to the rotational angular position around the C-axis of the supported workpiece.
A related art is disclosed in the distributed publication of Japanese Laid-Open Patent Publication No. 2005-324313 (corresponds to U.S. Pat. No. 7,118,453). This publication discloses a grinding method for grinding a shoulder portion of a workpiece by a rotational grinding wheel from a direction parallel to a rotational axis of the grinding wheel where the workpiece has a cylindrical portion and the shoulder portion extending from the cylindrical portion to a perpendicular direction to an axis of the cylindrical portion. In this method, there are two processes in a shoulder grinding, one of which is a first grinding process infeeding the grinding wheel along an oblique direction by the way of shortening a ground width of the shoulder portion in the axis direction according to approach the rotational axis of the workpiece, the other of which is a second grinding process infeeding the grinding wheel along the rotational axis toward the shoulder portion to grind the remaining of the grinding portion of the shoulder portion in the grinding along the oblique direction after the grinding wheel reaches a predetermined position of the cylindrical portion.
The another related art will be explained hereinafter in detail, it is well known conventional method, as shown in FIG. 1, to transfer and print the profile of a cutting tool 30, in this example the grinding wheel, to an arc curve portion of a crankpin 11 of the workpiece 10 having both end portions 11A and 11C whose diameter of a circumferential surface are gradually smaller in accordance with a distance from a shoulder portion to a central portion 11B of the workpiece to form an arc profile, and the central portion 11B whose diameter of the circumferential surface is constant. In this conventional method, a width 30 W of the cutting tool 30 is almost equal to a longitudinal distance 11W of the crankpin 11 and the profile of the circumferential surface 30A, 30B, 30C of the cutting tool 30 is transferred and copied to the profile of the circumferential surface 11A, 11B, 11C after cutting the workpiece 10 by the cutting tool 30. On this cutting method of the workpiece 10 shown in FIG. 1, the profile of the cutting tool 30 is pre-formed before cutting.
This conventional cutting method is performed by a numerical controller using a program. Plural programs are shown in FIG. 3 and a user-set-program (hereinafter called as user set program) is written as shown in FIG. 3. In FIG. 3, the program comprises a group of user set programs having single or plural user set programs and a group of axis driving programs prepared for each of driven axes. The axis driving program is input an amount of output command (hereinafter called as a control amount) output from a CPU of the numerical controller to a driving unit and the control amount is calculated by the user set program.
The user set program is written a program to calculate the control amount for single or plural axes identified by a user or an operator arbitrarily and therefore the user is free to write the user set program.
The axis driving program is prepared to drive the driving unit for the actual axis, that is a driving motor, and therefore it is corresponded to each of driving units. Besides, the user is not free to write the axis driving program.
Each of driving units is input the control amount (output command) from the correspondent axis driving program and controls in a feedback mode to compensate a difference between an output command and a position or rotational angle et al based on a detected signal from a correspondent position detector.
Where there are a plurality of user set programs, the CPU performs each of user set programs independently and in parallel. The control amount calculated by each of user set programs is input to an axis output program in parallel. Thereby, plural user set programs are simultaneously performed and each axis is controlled simultaneously.
Besides, each axis is identified by only one user set program individually. Therefore, where there are two user set programs PU1, PU2, the user can not identify the X-axis nor the C-axis to calculate the control amount in user set program US2 after the user has identified the X-axis or the C-axis in the user set program US1 to calculate the control amount.
As shown in FIG. 2, the CPU of the numerical controller reads a step N010 and recognizes an identification of a C-X profile motion start mode based on “G51” where “G51” is pre-registered as the C-X profile motion start mode. And also the CPU commands to rotate the crankshaft 10 at 60 rounds per minutes based on the “S60” and it recognizes an command to control a wheel head driving motor to position the surface of the grinding wheel 30 at the position along the X-axis according to the rotational angular position around the C-axis based on datum of the rotational angular position around the C-axis and the position along X-axis registered in a file “P2345” and it also calculates the control amount around C-axis and the control amount along X-axis. In the file “P2345” is registered a distance X (shown in FIG. 6B explained hereinafter) correspondent to a rotational angle θ in an each predetermined rotational angle.
The CPU of the numerical controller reads a next step N020 shown in FIG. 2, it recognizes an infeed mode based on “G01” where “G01” is pre-registered as the infeed mode and recognizes outside positioning mode according to a measured dimension based on “G31” by a sizing device that measures the dimension of the ground portion of the workpiece where “G31” is pre-registered as the outside positioning mode. And the CPU recognizes relative position command mode based on “G91×−0.2 F1.” where G91 is pre-registered as the relative position command mode and recognizes the command to infeed the grinding wheel 30 along the X-axis in the amount of 0.2 mm by the infeed speed of 1 mm/min, calculates the control amount of the wheel head along X-axis. The amount of “−0.2” means that the grinding wheel 30 is infed toward the crankshaft 10 at the amount of 0.2 mm. The CPU compounds the control amount calculated in Step N010 and the control amount calculated in Step N020 to input the resulted amount to an X-axis driving program Pjx. The control amount around C-axis calculated in Step N10 is input to a C-axis driving program Pjc.
Then, the CPU reads a next Step N030 based on an output signal from the sizing device where the output signal is shown in an address 98765.
Next, the CPU reads the Step N030 and recognizes both of the infeed mode and outside positioning command mode based on “G01” and “G31”. Then, it recognizes relative positioning command mode according to “G91” based on “G91×−0.02 F0.5” and recognizes the command to infeed the wheel head along the X-axis at the amount of 0.02 mm in the infeed speed 0.5 mm/min, calculating the control amount of the wheel head along X-axis. The CPU compounds the control amount calculated in Step N010 and the control amount calculated in Step N030 to input the resulted amount to the X-axis driving program Pjx. The control amount around C-axis calculated in Step N10 is input to the C-axis driving program Pjc.
Then, the CPU reads a next Step N040 based on an output signal from the sizing device where the output signal is shown in an address 98764.
Next, the CPU reads a Step N040 and recognizes a sparkout mode based on “G04” where “G04” is pre-registered as the sparkout mode. And, it recognizes the command to perform the sparkout motion at single revolution around the C-axis based on “P1”. The “sparkout” means to position the surface of the grinding wheel to the preset infeed position during stopping the infeed motion of the wheel head in order to perform a sparkout grinding based on a spring back of the workpiece because of the lack of rigidity of a wheel spindle and the workpiece during grinding, causing a final motion to make a smooth surface of the workpiece.
After the CPU performed the sparkout motion at the single revolution, it reads a Step N050 and recognizes a profile motion termination mode based on “G50” where the “G50” is pre-registered as the profile motion termination mode and it stops the C-X profile motion along the X-axis and around the C-axis.
In the above explained related art for cutting the crankpin 11 as shown in FIG. 1, there are two conventional ways to perform the grinding method described in the distributed publication of Tokkai 2005-324313, or the transferring and printing method of the profile of the cutting tool 30.
However, in the related art disclosed in the distributed publication of Tokkai 2005-324313, as shown in FIG. 4, the cutting tool is in-fed in quite large amount at the beginning grinding and this amount is gradually reduced so that it causes to appear an exceeded grinding load at the beginning grinding and therefore there is a possibility to make a bending of the workpiece and to make a grinding accuracy worse. In the first grinding process, the grinding load to the grinding wheel is suddenly maximum from zero and is gradually reduced in following the reduction of the grinding amount. Therefore, a wear of the grinding wheel is large because of sudden increase of the load in the beginning grinding to cause a life of the grinding wheel short.
And another related art of the transferring and printing method of the cutting tool 30 needs more labourer to re-dress the profile of the cutting tool 30 in order to re-fit the changed workpiece or to change the cutting tool 30 in a small lot of productions or in the large size of the changed workpiece to reduce a labour effectiveness.
Therefore, the inventors of the present invention think to adjust the change of the profiles and sizes of the crankpin without transferring and copying of the cutting tool 30 if it is achieved to move the cutting tool 30 along the arc profile of the crankpin in Z-axis and X-axis with the C-X profile motion by using the cutting tool having the smaller width 30W compared to a length 11W of the crankpin 11, as shown in FIG. 7. If the grinding load of the grinding wheel 30 is gradually increased from zero in no load, the life of the cutting tool 30 would become longer and the bending of the workpiece and the worse grinding accuracy would be restrained.
However, in the above-mentioned program writing method of the related numerical controller, it could not be performed for the program to write plural motions for one axis, that is the X-axis motions relating to the C-X profile motion moving along the X-axis according to the rotational angle around the C-axis, relating to the infeed motion to grind the diameter of the crankpin to a desired dimension along the X-axis, and relating to the X-axis motion corresponding to the moved distance along the Z-axis according to the arc profile of the crankpin.